1. Field of the Invention
The present invention relates to an objective lens drive apparatus configured to drive an objective lens that focuses a laser beam, an optical pickup that includes such an objective lens drive apparatus, and an information read/write apparatus that includes such an optical pickup.
2. Description of the Related Art
With the development of data digitizing techniques and data compression techniques, large-capacity optical disks such as the DVD (digital versatile disk) and BD (Blu-ray disk) are becoming widely used as recording media. Upon reading and writing information on such large capacity disks, a laser beam has to be accurately focused on tracks of the optical disk, which is rotated at a high speed. Therefore, an objective lens onto which the laser beam is focused has to be driven at a high speed in accordance with the deflection of the optical disk and/or the eccentricity of the tracks, for example.
An apparatus for driving such an objective lens is preferably arranged to have a movable part that is reduced in weight to enable the objective lens to be moved at a high speed and be capable of controlling high degree resonance of the mobile part resulting from the drive operations. In this regard, for example, Japanese Laid-Open Patent Publication No. 2001-331956 discloses a drive apparatus implementing the so-called moving magnet method to achieve advantageous characteristics with respect to high degree resonance, the apparatus also being configured to drive the objective lens at a high speed.
The drive apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-331956 implements measures for improving drive sensitivity for the objective lens by arranging drive magnets each facing one side and the other side of a coil to double the effective area of the coil on which electromagnetic forces act. However, in this drive apparatus, parts of the magnetic fields acting on the coil that are generated by the opposing magnets may cancel each other out. Also, it is noted that in this apparatus, a small magnetic piece is arranged within the drive coil, and the line of magnetic force from a drive magnetic field enters this magnetic piece of the drive coil from the N pole, exists the drive coil from a given location, and reenters the magnetic piece from the S pole. With such a configuration, although effective forces may be generated by the magnetic fields in the tangential directions of the magnets and their surrounding areas, undesired forces may be generated at other parts of the drive coil to thereby cause degradation in drive performance. Further, it is noted that since four drive magnets are arranged at two sides of a movable part in this drive apparatus, degradation of high degree resonance characteristics resulting from elastic deformation of the movable part may occur.